In 1980, a cross-sectional survey to measure the prevalence of dental caries and dental fluorosis was conducted in several study sites served by public water supplies that contained natural fluorides at approximately the optimum recommended concentration and at two, three and four times the optimum. Only children who were continuous residents since birth at each site and who used the public water supply as their primary source of drinking water were included in the survey. About 800 children, ages 8-15 years, were examined. Dental caries was assessed with the DMF surface index and dental fluorosis was measured traditionally with Dean's Index and with a newly developed tooth surface index of fluorosis (TSIF). Fluorosis was assessed independently in each child by each index. In addition, color photographs were taken to depict varying degrees of fluorosis.